qemuProcessVerifyHypervFeatures is supposed to check whether all requested hyperv features were actually honored by QEMU/KVM. This is done by checking the corresponding CPUID bits reported by the virtual CPU. In other words, it doesn't work for string properties, such as VIR_DOMAIN_HYPERV_VENDOR_ID (there is no CPUID bit we could check). We could theoretically check all 12 bits corresponding to the vendor string, but luckily we don't have to check the feature at all. If QEMU is too old to support hyperv features, the domain won't even start. Otherwise, it is always supported. Without this patch, libvirt refuses to start a domain which contains <features> <hyperv> <vendor_id state='on' value='...'/> </hyperv> </features> reporting internal error: "unknown CPU feature __kvm_hv_vendor_id. This regression was introduced by commit v3.1.0-186-ge9dbe7011, which (by fixing the virCPUDataCheckFeature condition in qemuProcessVerifyHypervFeatures) revealed an old bug in the feature verification code. It's been there ever since the verification was implemented by commit v1.3.3-rc1-5-g95bbe4bf5, which effectively did not check VIR_DOMAIN_HYPERV_VENDOR_ID at all. https://bugzilla.redhat.com/show_bug.cgi?id=1439424 Signed-off-by: Jiri Denemark <jdenemar(a)redhat.com&gt; --- BTW, I think this should be cherry-picked in v3.2-maint branch. src/qemu/qemu_process.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c index 18ff1e143..0f64200da 100644 --- a/src/qemu/qemu_process.c +++ b/src/qemu/qemu_process.c @@ -3793,6 +3793,10 @@ qemuProcessVerifyHypervFeatures(virDomainDefPtr def, int rc; for (i = 0; i < VIR_DOMAIN_HYPERV_LAST; i++) { + /* always supported string property */ + if (i == VIR_DOMAIN_HYPERV_VENDOR_ID) + continue; + if (def->hyperv_features[i] != VIR_TRISTATE_SWITCH_ON) continue; @@ -3821,13 +3825,13 @@ qemuProcessVerifyHypervFeatures(virDomainDefPtr def, case VIR_DOMAIN_HYPERV_SYNIC: case VIR_DOMAIN_HYPERV_STIMER: case VIR_DOMAIN_HYPERV_RESET: - case VIR_DOMAIN_HYPERV_VENDOR_ID: virReportError(VIR_ERR_CONFIG_UNSUPPORTED, _("host doesn't support hyperv '%s' feature"), virDomainHypervTypeToString(i)); return -1; /* coverity[dead_error_begin] */ + case VIR_DOMAIN_HYPERV_VENDOR_ID: case VIR_DOMAIN_HYPERV_LAST: break; } -- 2.12.2